In the web hosting business, you're not really expecting people to buy more than one of your servers (VPS or otherwise), so buy one, get one free doesn't really make much sense for us. What we do though is that we offer a percentage off, and then list the price with the percentage off in our advertisements. It's kind of a best of both worlds situation. The thing with percentages though is that it's easier to spread across multiple items, instead of listing the prices (which can take a lot of space which you may not have in an advertisement).